N-phenyltetrahydrophthalimides

ABSTRACT

N-Phenyltetrahydrophtalimides of the general formula I ##STR1## where R 1  is hydrogen or halogen, R 2  is halogen, R 3  is hydrogen or C 1  -C 4  -alkyl, R 4  is unsubstituted or C 1  -C 3  -alkoxy-substituted C 1  -C 8  -alkyl, C 3  -C 4  -alkenyl or C 3  -C 4  -alkynyl, and R 5  is hydrogen or C 1  -C 4  - alkyl, methods for their manufacture, and their use as herbicides.

N-Aryl-substituted tetrahydrophthalimides which have a herbicidal action are known. For example, EP-A-207,894 describes tetrahydrophthalimides of of the formula I' ##STR2## where the radicals have for example the following meanings:

R^(a) and R^(b) are identical or different and each is hydrogen or halogen;

R^(c) and R^(d) together denote, inter alia, a substituted or unsubstituted C₂ -C₃ -alkylene bridge; and

R^(e) is, inter alia, hydrogen, cyano or C₁ -C₄ -alkyl.

However, the action of these compounds is unsatisfactory at low application rates.

The object of the invention was therefore to provide N-phenyltetrahydrophthalimide compounds which have, at low application rates, a better action on unwanted plants without damaging crop plants.

We have now found that tetrahydrophthalimides of the formula I ##STR3## where R¹ is hydrogen or halogen, R² is halogen, R³ is hydrogen or C₁ -C₄ -alkyl, R⁴ is unsubstituted or C₁ -C₃ -alkoxy-substituted C₁ -C₈ -alkyl, C₃ -C₄ -alkenyl or C₃ -C₄ -alkynyl, and R⁵ is hydrogen or C₁ -C₄ -alkyl, have an advantageous herbicidal action particularly when applied postemergence, and are selective in a number of crop plants.

By halogen, we mean fluorine, chlorine and bromine, halogen for R¹ preferably being fluorine and for R² preferably chlorine.

The term alkyl embraces straight-chain and branched radicals, e.g., methyl, ethyl, n-propyl and isopropyl.

The alkenyl and alkynyl radicals may also be straight-chain or branched. Examples of alkenyl radicals in formula I are 2-propenyl, 2-butenyl, 3-butenyl, and 2-isobutenyl, especially 2-propenyl and 2-butenyl; alkynyl radicals are usually propargyl, 2-butynyl and 3-butynyl.

The invention embraces the enantiomers, the diastereomers and mixtures thereof.

The N-substituted tetrahydrophthalimides are obtainable from 3,4,5,6-tetrahydrophthalic anhydride and an aniline of the formula V, e.g., in a solvent at a temperature of from 20° to 200° C., preferably 40° to 150° C. Suitable solvents are for example lower alkanoic acids such as glacial acetic acid or propionic acid, or aprotic solvents such as toluene or xylene in the presence of acidic catalysts such as aromatic sulfonic acids.

Preferred compounds I are those in which R¹ is hydrogen or fluorine, R² is chlorine, R³ is C₁ -C₂ -alkyl, R⁴ is C₁ -C₄ -alkyl, C₃ -C₄ -alkenyl or C₃ -C₄ -alkynyl and R⁵ is hydrogen or methyl.

The anilines of the formula V are obtained for example by reducing a nitrobenzene IV having the appropriate acetal structure by means of reducing agents such as iron or tin(II) salts. ##STR4##

The reduction can also be carried out as a catalytic hydrogenation with a noble metal catalyst such as platinum or palladium, or with Raney nickel under relatively mild conditions.

Nitroacetals IV are accessible by reaction of an appropriate benzaldehyde II in an inert solvent in the presence of an acid with a diol of the formula III: ##STR5##

The recommendations given in the examples below were employed to obtain further compounds of the general formula I using different starting compounds. These compounds and their physical data are given in the following table. Compounds without any physical data may be obtained from the corresponding materials in analogous manner. Because of their close structural similarity to the manufactured and investigated compounds they are expected to have a similar action.

EXAMPLE ##STR6##

(a) 19.4 g of n-butyl 2,3-dihydroxyisobutyrate is added to 18.6 g of 2-chloro-5-nitrobenzaldehyde and 0.5 g of p-toluenesulfonic acid in 250 ml of toluene, and the mixture is refluxed for 5 hours using a water separator. The mixture is cooled, the solvent is removed and the remainder is dried in a high vacuum. There is obtained 35 g of 3-(5-methyl-5-n-butyloxycarbonyl-1,3-dioxolan-2-yl)-4-chloronitrobenzene (oil).

(b) While refluxing, 34.4 g of the above nitro compound in 20 ml of methanol is added to a mixture of 16.8 g of iron powder in 30 ml of methanol and 75 ml of glacial acetic acid. The mixture is refluxed for 2 hours. After cooling, 250 ml of water is added and the mixture is subjected to suction filtration. The filtrate is extracted three times, each time with 100 ml of ethyl acetate, dried, concentrated and dried in a high vacuum. There is obtained 31 g of 3-(5-methyl-5-n-butyloxycarbonyl-1,3-dioxolan-2-yl)-4-chloroaniline (oil).

(c) 15.7 g of the above aniline and 7.6 g of cyclohexene-1,2-dicarboxylic anhydride are refluxed for 5 hours in 150 ml of glacial acetic acid. After cooling, 150 ml of water is added, followed by extraction twice with 100 ml of methylene chloride, drying and removal of the solvent. The product is purified by chromatography and dried in a high vacuum. There is obtained 9.0 g of N-[3-(5-methyl-5-n-butyloxycarbonyl-1,3-dioxolan-2-yl)-4-chlorophenyl]-3.4.5.6-tetrahydrophthalimide (oil) (Table 1, no. 1.027).

Table 1 contains further examples of active ingredients which can be prepared by this synthesis principle.

                                      TABLE 1                                      __________________________________________________________________________      ##STR7##                                                                      No.                                                                               R.sup.1                                                                           R.sup.3                                                                             R.sup.4        mp [°C.]                                                                     IR [cm.sup.-1 ]                                 __________________________________________________________________________     1.001                                                                             H  H    CH.sub.3                                                            1.002                                                                             F  H    CH.sub.3                                                            1.003                                                                             H  CH.sub.3                                                                            CH.sub.3       oil  1715, 1481, 1377, 1088                          1.004                                                                             F  CH.sub.3                                                                            CH.sub.3                                                            1.005                                                                             H  CH.sub.2 CH.sub.3                                                                   CH.sub.3       oil  2938, 1715, 1481, 1378, 1088                    1.006                                                                             F  CH.sub.2 CH.sub.3                                                                   CH.sub.3                                                            1.007                                                                             H  H    CH.sub.2 CH.sub.3                                                   1.008                                                                             F  H    CH.sub.2 CH.sub.3                                                   1.009                                                                             H  CH.sub.3                                                                            CH.sub.2 CH.sub.3                                                                             oil  1715, 1480, 1376, 1088                          1.010                                                                             F  CH.sub.3                                                                            CH.sub.2 CH.sub.3                                                                             oil  1720, 1500, 1422, 1082                          1.011                                                                             H  CH.sub. 2 CH.sub.3                                                                  CH.sub.2 CH.sub.3                                                                             oil  2938, 1715, 1480, 1377, 1089                    1.012                                                                             F  CH.sub.2 CH.sub.3                                                                   CH.sub.2 CH.sub.3                                                                             oil  1721, 1500, 1422, 1083                          1.013                                                                             H  H    (CH.sub.2).sub.2 CH.sub.3                                           1.014                                                                             F  H    (CH.sub.2).sub.2 CH.sub.3                                           1.015                                                                             H  CH.sub.3                                                                            (CH.sub.2).sub.2 CH.sub.3                                                                     oil  2929, 1716, 1479, 1377, 1089                    1.016                                                                             F  CH.sub.3                                                                            (CH.sub.2).sub.2 CH.sub.3                                                                     oil  1720, 1500, 1422, 1082                          1.017                                                                             H  CH.sub.2 CH.sub.3                                                                   (CH.sub.2).sub.2 CH.sub.3                                                                     oil  2938, 1716, 1481, 1378, 1089                    1.018                                                                             F  CH.sub.2 CH.sub.3                                                                   (CH.sub.2).sub.2 CH.sub.3                                                                     oil  1721, 1500, 1422, 1083                          1.019                                                                             H  H    CH(CH.sub.3).sub.2                                                  1.020                                                                             F  H    CH(CH.sub.3).sub.2                                                  1.021                                                                             H  CH.sub.3                                                                            CH(CH.sub.3).sub.2                                                  1.022                                                                             F  CH.sub.3                                                                            CH(CH.sub.3).sub.2                                                  1.023                                                                             H  CH.sub.2 CH.sub.3                                                                   CH(CH.sub.3).sub.2                                                  1.024                                                                             F  CH.sub.2 CH.sub.3                                                                   CH(CH.sub.3).sub.2                                                  1.025                                                                             H  H    (CH.sub.2).sub.3 CH.sub.3                                           1.026                                                                             F  H    (CH.sub.2).sub.3 CH.sub.3                                           1.027                                                                             H  CH.sub.3                                                                            (CH.sub.2).sub.3 CH.sub.3                                                                     oil  2958, 1716, 1481, 1377, 1088                    1.028                                                                             F  CH.sub.3                                                                            (CH.sub.2).sub.3 CH.sub.3                                                                     oil  2958, 1721, 1500, 1423, 1082                    1.029                                                                             H  CH.sub.2 CH.sub.3                                                                   (CH.sub.2).sub.3 CH.sub.3                                                                     oil  2960, 1716, 1480, 1378, 1089                    1.030                                                                             F  CH.sub.2 CH.sub.3                                                                   (CH.sub.2).sub.3 CH.sub.3                                                                     oil  2960, 1721, 1500, 1422                          1.031                                                                             H  CH.sub.3                                                                            CH.sub.2 CH(CH.sub.3).sub.2                                                                   oil  2960, 1718, 1481, 1378, 1088                    1.032                                                                             F  CH.sub.3                                                                            CH.sub.2 CH(CH.sub.3).sub.2                                         1.033                                                                             H  CH.sub.2 CH.sub.3                                                                   CH.sub.2 CH(CH.sub.2 CH.sub.3)(CH.sub.2).sub.3 CH.sub.3                                       oil  2932, 1717, 1481, 1378, 1089                    1.034                                                                             F  CH.sub.2 CH.sub.3                                                                   CH.sub.2 CH(CH.sub.2 CH.sub.3)(CH.sub.2).sub.3 CH.sub.3             __________________________________________________________________________

                  TABLE 2                                                          ______________________________________                                          ##STR8##                                                                      No.  R.sup.1                                                                               R.sup.3                                                                               R.sup.4 mp [°C.]                                                                       IR [cm.sup.-1 ]                              ______________________________________                                         2.001                                                                               H      CH.sub.3                                                                              CH.sub.3                                                    2.002                                                                               F      CH.sub.3                                                                              CH.sub.3                                                    2.003                                                                               H      CH.sub.3                                                                              CH.sub.2 CH.sub.3                                           2.004                                                                               F      CH.sub.3                                                                              CH.sub.2 CH.sub.3                                           2.005                                                                               H      CH.sub.3                                                                              (CH.sub.2).sub.2 CH.sub.3                                   2.006                                                                               F      CH.sub.3                                                                              (CH.sub.2).sub.2 CH.sub.3                                   2.007                                                                               H      H      CH(CH.sub.3).sub.2                                                                     oil    2936, 1717, 1418, 1376                                                         1101                                         2.008                                                                               F      H      CH(CH.sub.3).sub.2                                          2.009                                                                               H      H      (CH.sub.2).sub.3 CH.sub.3                                                              oil    2958, 1715, 1480, 1378                                                         1100                                         2.010                                                                               F      H      (CH.sub.2).sub.3 CH.sub.3                                   2.011                                                                               H      H      CH.sub.3                                                                               oil    1715, 1481, 1378, 1104                       2.012                                                                               F      H      CH.sub.3                                                    2.013                                                                               H      H      (CH.sub.2).sub.2 CH.sub.3                                   2.014                                                                               F      H      (CH.sub.2).sub.2 CH.sub.3                                   ______________________________________                                    

                  TABLE 3                                                          ______________________________________                                          ##STR9##                                                                      No.  R.sup.3                                                                               R.sup.4   R.sup.5                                                                             mp [°C.]                                                                       IR [cm.sup.-1 ]                              ______________________________________                                         3.001                                                                               H      CH.sub.3  H                                                        3.002                                                                               CH.sub.3                                                                              CH.sub.3  H                                                        3.003                                                                               H      CH.sub.3  CH.sub.3                                                 3.004                                                                               CH.sub.3                                                                              CH.sub.3  CH.sub.3                                                 3.005                                                                               H      CH.sub.2 CH.sub.3                                                                        H                                                        3.006                                                                               CH.sub.3                                                                              CH.sub.2 CH.sub.3                                                                        H                                                        3.007                                                                               H      CH.sub.2 CH.sub.3                                                                        CH.sub.3                                                 3.008                                                                               CH.sub.3                                                                              CH.sub.2 CH.sub.3                                                                        CH.sub.3                                                 3.009                                                                               H      (CH.sub.2).sub.2 CH.sub.3                                                                H                                                        3.010                                                                               CH.sub.3                                                                              (CH.sub.2).sub.2 CH.sub.3                                                                CH.sub.3                                                 3.011                                                                               H      (CH.sub.2).sub.2 CH.sub.3                                                                CH.sub.3                                                 3.012                                                                               CH.sub.3                                                                              (CH.sub.2 ).sub.2 CH.sub.3                                                               CH.sub.3                                                 3.013                                                                               H      CH(CH.sub.3).sub.2                                                                       H                                                        3.014                                                                               CH.sub.3                                                                              CH(CH.sub.3).sub.2                                                                       H                                                        3.015                                                                               H      CH(CH.sub.3).sub.2                                                                       CH.sub.3                                                                            oil    2978, 1720, 1512, 1437,                                                        1097, 1068                                   3.016                                                                               CH.sub.3                                                                              CH(CH.sub.3).sub.2                                                                       CH.sub.3                                                 3.017                                                                               H      (CH.sub.2).sub.3 CH.sub.3                                                                H                                                        3.018                                                                               CH.sub.3                                                                              (CH.sub.2).sub.3 CH.sub.3                                                                H    oil    1720, 1512, 1437, 1132                       3.019                                                                               H      (CH.sub.2).sub.3 CH.sub.3                                                                CH.sub.3                                                 3.020                                                                               CH.sub.3                                                                              (CH.sub.2).sub.3 CH.sub.3                                                                CH.sub.3                                                 ______________________________________                                    

The herbicidal agents, or the active ingredients on which they are based, may be applied pre- or postemergence. If certain crop plants tolerate the active ingredients less well, application techniques may be used in which the herbicidal agents are sprayed from suitable equipment in such a manner that the leaves of sensitive crop plants are if possible not touched, and the agents reach the soil or the unwanted plants growing beneath the crop plants (post-directed, lay-by treatment).

The application rates depend on the objective to be achieved, the time of the year, the plants to be combated and their growth stage, and are from 0.005 to 3.0, preferably 0.01 to 0.5, kg/ha.

The action of the active ingredients of the formula I on the growth of plants is illustrated in greenhouse experiments.

The vessels employed were plastic flowerpots having a volume of 300 cm³ and filled with a sandy loam containing about 3.0% humus. The seeds of the test plants were sown separately, according to species.

For the postemergence treatment, either plants which had been sown in the pots and grown there were selected, or they were cultivated separately as seedlings and transplanted to the pots a few days before being treated.

Depending on growth form, the plants were grown to a height of from 3 to 15 cm before being treated with the active ingredients which were suspended or emulsified in water and sprayed through finely distributing nozzles. The application rate for postemergence treatment was 0.06 kg/ha.

The pots were set up in the greenhouse, species from warmer climates in warmer areas (20° to 35° C.) and species from moderate climates at 10° to 20° C. The experiments were run for from 2 to 4 weeks. During this time the plants were tended and their reactions to the various treatments assessed.

The assessment scale was 0 to 100, 100 denoting nonemergence or complete destruction of at least the visible plant parts, and 0 denoting no damage or normal growth.

The plants used in the greenhouse experiments belonged to the following species:

    ______________________________________                                         CODE    Botanical name    Common name                                          ______________________________________                                         ABUTH   Abutilon theophrasti                                                                             velvet leaf                                          AMARE   Amaranthus spp.   pigweed                                              CHYCO   Chrysanthemum corinarium                                                                         crown daisy                                          DEDTO   Desmodium tortuosum                                                                              Florida beggarweed                                   GALAP   Galium aparine    catchweed bedstraw                                   IPOSS   Ipomoea spp.      morningglory                                         LAMAM   Lamium amplexicaule                                                                              henbit                                               MERAN   Mercurialis annua annual mercury                                       POLPE   Polygonum persicaria                                                                             ladysthumb                                           SINAL   Sinapis alba      white mustard                                        SOLNI   Solanum nigrum    black nightshade                                     STEME   Stellaria media   chickweed                                            TRZAS   Triticum aestivum spring wheat                                         TRZAW   Triticum aestivum wheat                                                VERSS   Veronica spp.     speedwell                                            ZEAMX   Zea mays          Indian corn                                          ______________________________________                                    

In view of the numerous application methods possible, the compounds according to the invention, or agents containing them, may be used in a large number of crop plants for removing unwanted plants. The following crops are examples:

    ______________________________________                                         Botanical name        Common name                                              ______________________________________                                         Allium cepa           onions                                                   Ananas comosus        pineapples                                               Arachis hypogaea      peanuts (groundnuts)                                     Asparagus officinalis asparagus                                                Avena sativa          oats                                                     Beta vulgaris spp. altissima                                                                         sugarbeets                                               Beta vulgaris spp. rapa                                                                              fodder beets                                             Beta vulgaris spp. esculenta                                                                         table beets, red beets                                   Brassica napus var. napus                                                                            rapeseed                                                 Brassica napus var. napobrassica                                                                     swedes                                                   Brassica napus var. rapa                                                                             turnips                                                  Brassica rapa var. silvestris                                                  Camellia sinensis     tea plants                                               Carthamus tinctorius  safflower                                                Carya illinoinensis   pecan trees                                              Citrus limon          lemons                                                   Citrus maxima         grapefruits                                              Citrus reticulata     mandarins                                                Citrus sinensis       orange trees                                             Coffea arabica (Coffea canephora,                                              Coffea liberica)      coffee plants                                            Cucumis melo          melons                                                   Cucumis sativus       cucumbers                                                Cynodon dactylon      Bermudagrass                                             Daucus carota         carrots                                                  Elais guineensis      oil palms                                                Fragaria vesca        strawberries                                             Glycine max           soybeans                                                 Gossypium hirsutum (Gossypium arboreum,                                                              cotton                                                   Gossypium herbaceum, Gossypium vitifolium)                                     Helianthus annuus     sunflowers                                               Helianthus tuberosus  Jerusalem artichoke                                      Hevea brasiliensis    rubber plants                                            Hordeum vulgare       barley                                                   Humulus lupulus       hops                                                     Ipomoea batatas       sweet potatoes                                            Juglans regia        walnut trees                                             Linum usitatissimum   flax                                                     Lycopersicon lycopersicum                                                                            tomatoes                                                 Malus spp.            apple trees                                              Manihot esculenta     cassava                                                  Medicago sativa       alfalfa (lucerne)                                        Mentha piperita       peppermint                                               Musa spp.             banana plants                                            Nicotiana tabacum (N. rustica)                                                                       tobacco                                                  Olea europaea         olive trees                                              Oryza sativa          rice                                                     Phaseolus lunatus     limabeans                                                Phaseolus mungo       mungbeans                                                Phaseolus vulgaris    snapbeans, green                                                               beans, dry beans                                         Pennisetum glaucum    pearl millet                                             Petroselinum crispum spp. tuberosum                                                                  parsley                                                  Picea abies           Norway spruce                                            Abies alba            fir trees                                                Pinus spp.            pine trees                                               Pisum sativum         English peas                                             Prunus avium          cherry trees                                             Prunus domestica      plum trees                                               Prunus dulcis         almond trees                                             Prunus persica        peach trees                                              Pyrus communis        pear trees                                               Ribes sylvestre       redcurrants                                              Ribes uva-crispa      gooseberries                                             Ricinus communis      castor-oil plants                                        Saccharum officinarum sugar cane                                               Secale cereale        rye                                                      Sesamum indicum       sesame                                                   Solanum tuberosum     Irish potatoes                                           Sorghum bicolor (s. vulgare)                                                                         sorghum                                                  Sorghum dochna        sorgo                                                    Theobroma cacao       cacao plants                                             Trifolium pratense    red clover                                               Triticum aestivum     wheat                                                    Vaccinium corymbosum  blueberries                                              Vaccinium vitis-idaea cranberries                                              Vicia faba            tick beans                                                Vigna sinensis (V. unguiculata)                                                                     cow peas                                                 Vitis vinifera        grapes                                                   Zea mays              Indian corn, sweet                                                             corn, maize                                              ______________________________________                                    

To increase the spectrum of action and to achieve synergistic effects, the N-phenyltetrahydrophthalimides of the formula I may be mixed with each other, or mixed and applied together with numerous representatives of other herbicidal or growth-regulating active ingredient groups. Examples of suitable components are diazines, 4H-3,1-benzoxazine derivatives, benzothiadiazinones, 2,6-dinitroanilines, N-phenylcarbamates, thiolcarbamates, halocarboxylic acids, triazines, amides, ureas, diphenyl ethers, triazinones, uracils, benzofuran derivatives, cyclohexane-1,3-dione derivatives, quinolinecarboxylic acids, etc.

It may also be useful to apply the N-phenyltetrahydrophthalimides of the formula I, either alone or in combination with other herbicides, in admixture with other crop protection agents, e.g., agents for combating pests or phytopathogenic fungi or bacteria. The compounds may also be mixed with solutions of mineral salts used to remedy nutritional or trace element deficiencies. Non-phytotoxic oils and oil concentrates may also be added.

                  TABLE 4                                                          ______________________________________                                         Herbicidal action of compound no. 1.027 on postemergence                       application of 0.06 kg/ha in the greenhouse                                    Test plants   Damage (%)                                                       ______________________________________                                         ABUTH         100                                                              AMARE         100                                                              DEDTO         100                                                              GALAP          98                                                              IPOSS         100                                                              MERAN         100                                                              SOLNI         100                                                              ______________________________________                                    

                  TABLE 5                                                          ______________________________________                                         Herbicidal action and tolerance by a crop on postemergence                     application of 0.03 kg/ha of compound no. 1.027                                Test plants   Damage (%)                                                       ______________________________________                                         GALAP         100                                                              LAMAM         100                                                              MERAN         100                                                              POLPE         100                                                              SINAL          95                                                              STEME         100                                                              TRZAW          0                                                               VERSS         100                                                              ______________________________________                                    

Examples demonstrating the control of unwanted broadleaved plants and tolerance by a crop on postemergence application of 0.03 kg/ha in the greenhouse.

                                      TABLE 6                                      __________________________________________________________________________      ##STR10##                                                                     Comp. no.                                                                            R.sup.1                                                                          R.sup.2                                                                          R.sup.3                                                                          R.sup.4                                                                              R.sup.5                                                                           TRZAS                                                                               CHYCO                                                                               SOLNI                                                                               GALAP                                                                               STEME                                 __________________________________________________________________________     2.007 H Cl                                                                               H CH(CH.sub.3).sub.2                                                                   CH.sub.3                                                                          10   100  100  100   90                                   2.009 H Cl                                                                               H (CH.sub.2).sub.3 CH.sub.3                                                            CH.sub.3                                                                          10   100  100  100  100                                   __________________________________________________________________________

                                      TABLE 7                                      __________________________________________________________________________      ##STR11##                                                                     Comp. no.                                                                            R.sup.1                                                                          R.sup.2                                                                          R.sup.3                                                                           R.sup.4 R.sup.5                                                                          ZEAMX                                                                               CHYCO                                                                               LAMAM                                                                               SOLNI                                                                               STEME                               __________________________________________________________________________     1.031 H Cl                                                                               CH.sub.3                                                                          CH.sub.2 CH(CH.sub.3).sub.2                                                            H 0    100  100  100  100                                 __________________________________________________________________________

                                      TABLE 8                                      __________________________________________________________________________      ##STR12##                                                                     Comp. no.                                                                            R.sup.1                                                                          R.sup.2                                                                          R.sup.3                                                                             R.sup.4                                                                           R.sup.5                                                                          TRZAS                                                                               CHYCO                                                                               SOLNI                                                                               VERSS                                       __________________________________________________________________________     1.005 H Cl                                                                               CH.sub.2 CH.sub.3                                                                   CH.sub.3                                                                          H 10   100  100  100                                         __________________________________________________________________________ 

We claim:
 1. An N-tetrahydrophthalimide of the general formula ##STR13## where R¹ is hydrogen or halogen, R² is halogen, R³ is hydrogen or C₁ -C₄ -alkyl, R⁴ is unsubstituted or C₁ -C₃ -alkoxy-substituted C₁ -C₈ -alkyl, C₃ -C₄ -alkenyl or C₃ -C₄ -alkynyl, and R⁵ is hydrogen or C₁ -C₄ -alkyl, independently of the steric configuration.
 2. A herbicidal agent containing a compound of the formula as set forth in claim 1, and conventional inert auxiliaries, extenders and diluents.
 3. A process for combating the growth of unwanted plants, wherein a herbicidally effective amount of an N-tetrahydrophthalimide as set forth in claim 1 is allowed to act on the plants and their habitat.
 4. An N-tetrahydrophthalimide of the general formula ##STR14## where R¹ is hydrogen or halogen, R² is halogen, R³ is C₁ -C₄ -alkyl, R⁴ is unsubstituted or C₁ -C₃ -alkoxy substituted C₁ -C₈ -alkyl, C₃ -C₄ -alkenyl or C₃ -C₄ -alkynyl, and R⁵ is hydrogen or C₁ -C₄ -alkyl, independently of steric configuration. 